Main.hs

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE ScopedTypeVariables #-}

module Main where

import Data.Reflection

newtype QDouble = QDouble Double
newtype Step = Step Double

instance Given Step => Eq QDouble where
  QDouble x == QDouble y = abs (x - y) < s
    where Step s = given

main :: IO ()
main = do
  n :: Double <- read <$> getLine
  print $ give (Step n) $ QDouble 0.5 == QDouble 0.6